Алгебра: cos (arcsin (-1/2) - arcsin1)

Arcsin (-1/2) = - π/6, так как sin (-π/6) = - 1/2 и - π/6 ∈[ - π/2; π/2]

arcsin 1 = π/2, так как sin (π/2) = 1 и π/2 ∈[ - π/2; π/2]

arcsin (-1/2) - arcsin 1 = - π/6 - π/2 = - 4π/6=-2π/3

cos (arcsin (-1/2) - arcsin 1) = cos (-2π/3) = cos (2π/3) = - 1/2